WASHINGTON (Reuters) - Obesity causes more than 100,000 cases of cancer in the United States each year -- and the number will likely rise as Americans get fatter, researchers said on Thursday.

Having too much body fat causes nearly half the cases of endometrial cancer -- a type of cancer of the uterus -- and a third of esophageal cancer cases, the American Institute for Cancer Research said.

Cancer is the second-leading cause of death in the United States after heart disease. The American Cancer Society projects that 1.47 million people will be diagnosed with cancer this year and 562,000 will die of it.

More than 26 percent of Americans are obese, defined as having a body mass index of 30 or higher. BMI is equal to weight in kilograms divided by height in meters squared. A person 5 feet 5 inches tall (165 cm) becomes obese at 180 pounds (82 kg).

Additionally, nearly a third of Americans are overweight, defined as having a BMI of 25 to 30.

The study combined findings from AICR research linking diet, physical activity and fatness with cancer risk with national surveys on obesity and cancer incidence.

"We then worked out the percentage of those specific cancers that would be prevented if everyone in the United States maintained a healthy weight," the group said in a statement.

Here are some of its estimates of cancer types that could be prevented annually if Americans stayed slender:

* Esophageal - 35 percent of cases or 5,800 people

* Pancreatic - 28 percent or 11,900

* Gallbladder - 21 percent or 2,000

* Colon - 9 percent or 13,200

* Breast - 17 percent or 33,000

* Endometrium - 49 percent or 20,700

* Kidney - 24 percent or 13,900

In July, federal and other researchers estimated that obesity-related diseases account for nearly 10 percent of all medical spending in the United States or an estimated $147 billion a year.